Multiple brush development

ABSTRACT

Two or more brushes are placed adjacent to and in mesh with each other and a surface bearing a latent electrostatic image to form a high-speed development system. Adjacent development brushes in the system are rotated at different speeds relative to one another to create a swirling motion during development. The primary brush in the system is the brush which initially contacts the latent image as it passes the development area and is, preferably, the only brush in the system which is loaded with toner by external means, the other brushes in the system receiving toner as a result of their meshing one with another.

United States Patent 9/ 1963 Bogdonoff et al.

IBM Technical Disclosure Bulletin, Vol. 2, No. 2, pgs. 4 & 5

Aug. 1959 Development of Electrostatic lmages Primary Examiner-WilliamD. Martin Assistant Examiner-M. Sofocleous Attorneys-Stanley Z. Cole andNorman E. Schrader ABSTRACT: Two or more brushes are placed adjacent toand in mesh with each other and a surface bearing a latent electrostaticimage to fonn a high-speed development system. Adjacent developmentbrushes in the system are rotated at different speeds relative to oneanother to create a swirling motion during development. The primarybrush in the system is the brush which initially contacts the latentimage as it passes the development area and is, preferably, the onlybrush in the system which is loaded with toner by external means, theother brushes in the system receiving toner as a result of their meshingone with another.

PATENIEBMN 4D?! INVENTOR. ERNEST A. WEILER A? T TORNE VS MULTIPLE BRUSHDEVELOPMENT This application is a continuation of my application, Ser.No. 659,518, filed Aug. 9, 1967, and now abandoned.

In many copying techniques, such as xerography, a latent image is firstformed on a recording surface and then developed with a markingmaterial. In the case of xerography the marking material normally usedin a finely divided colored material called toner. When developing alatent image with toner a well-known technique is to pass a brush loadedwith charged toner particles across the surface bearing the latentimage. The charged toner particles, bearing a charge which has adifferent potential compared to the portions of the latent image wherethe toner is deposited, are removed from the brush and adhere to therecording member in imagewise configuration. The brush used may be anysuitable type which can be loaded with toner particles such as amagnetic brush, fur brush, a brush made with cloth such as velvet havinga fibrous surface or other similar material bearing a multiplicity ofelongated carrier members on a surface.

In order to assure good quality in this development process it isdesirable to maintain a large contact area between the brush carryingthe toner particles and the surface being developed, and this isespecially desirable when developing an image which requires large solidarea coverage. Numerous devices have been conceived to assure suchquality in the xerographic process. For instance, instead of using acylindrical brush for development, belts have been used to carry tonerparticles to the latent image. Such belts normally are used with adrum-shaped photosensitive surface and consist of a backing memberhaving numerous bristles or fibers which carry toner particles to thesurface being developed. The belt is supported and driven by a series ofrollers, or the like, while a portion of its outer periphery maintainscontact with the latent image. When the belt has tangential contact withthe drum surface the resulting image quality is sufficient forrelatively slow development speeds only, and as the development speed isincreased, quality becomes inferior.

To increase contact area between the belt and surface bearing the latentimage in high-speed systems, the belt has been wrapped around the drumso that it maintains more than tangential contact with the drum surface.However, when this is done other serious problems arise which tend tominimize the benefit of increased contact between belt and drum. Onedisadvantage is that it is difficult to have the belt assume the precisearc necessary in order to maintain even contact with the drum. Inaddition, it is a difficult task to have every portion of the belt whichis adjacent the drum maintain the same degree of contact pressure on thedrum which is essential to good development.

When a cylinder-shaped brush is used to develop latent images, thequality of solid area coverage is dependent upon the contact areabetween the brush and the surface, and their relative speeds. As thespeed of the surface bearing the latent image increases, solid areacoverage can be maintained by increasing the diameter of the brush sothat there is a greater portion of the periphery of the brush in contactwith the surface. If cylindrical brushes of a large diameter were usedto assure adequate contact for high-speed drums, the development systemwould not be feasible because of space considerations and severevibration and balance problems.

Another alternative in brush design when the speed of development isincreased is to use a brush of relatively small diameter which rotatesat a very high velocity. However, it is generally undesirable to rotatethe brush at very high speeds since the brush would be difficult to loadwith toner particles and such high speeds would generate an excessivetoner powder cloud.

It has been found that by using a multitude of brushes placed adjacentone another and rotating them at difierent speeds in high-speeddevelopment the increased contact area between the brushes and thelatent images results in improved image quality. Accordingly, it is anobject of this invention to improve apparatus for developing latentelectrostatic charge patterns.

It is a further object to improve the apparatus for develop ing latentelectrostatic images to assure good solid area coverage.

A still further object is to improve the apparatus for developing latentelectrostatic images to render high-quality images in a high-speeddevelopment system.

The development apparatus in this invention requires the use of two ormore brushes placed adjacent each other in contact with the surfacebeing developed. Adjacent brushes in the system rotate at differentrates of speed thereby approximating a swirling action duringdevelopment. In one embodiment of the invention a series of rotatingbrushes are placed around a drum-shaped, photosensitive surface adjacentto and in mesh with each other. The primary brush in the group is theone located nearest the lowest point on the photosensitive surface whilethe remainder of the brushes in the group are stacked above the primarybrush in the direction that the photosensitive surface travels duringdevelopment. Since the fibers of each brush mesh with those adjacent toit, toner particles are passed from the primary brush to the next brushin the group and so forth so that all brushes become loaded with toneras they rotate. In addition, the meshing of the brushes creates a smallpowder cloud which enhances development of solid areas. As thephotosensitive surface travels past the group of brushes, it has theopportunity to pick up toner from all the brushes. The number of brushesused in any particular system is a function of the speed that thephotosensitive surface travels, more brushes being desirable as thespeed of the photosensitive surface increases.

For a better understanding of the invention as well as other objects andfurther features thereof, reference is bad to the following detaileddescription of the invention to be used in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a schematic illustration showing a typical xerographic devicein which the present development apparatus is used.

FIG. 2 is a schematic view of the development apparatus showing thearrangement of the brushes relative to each other, the photosensitivesurface, and the toner hopper.

Referring now to the drawings, FIG. 1 shows a typical xerographicmachine in which the present development apparatus can be used. Theprinciple element of the machine is photosensitive member 11. Thismember consists of drum [2 which is driven about shaft 16 by a motor(not shown). The drum is covered with layer 13 of electricallyconductive material which, in turn, is covered on its outer surface withlayer 14, a photoconductive insulating material such as vitreousselenium. An electrostatic latent image is formed on member 11 bypassing it adjacent sensitizing station 24 and exposing station 17. Thesensitizing station consists of any suitable means for placing a uniformcharge on layer 14 such as corona charging device 26. The exposingstation comprises light source 23 and lens 18, and transparency l9feedably disposed between the light source and lens. The transparency isfed from reel 21 through the beam of light generated by source 23 andthen rewound on reel 22 after being exposed. The light source,transparency and lens working in combina tion project on thephotosensitive member an optical image whose movement is synchronizedwith that of the drum. The projected optical image causes selectivecharge dissipation on illuminated areas of layer 14, thus forming alatent electrostatic image. Other means of forming electrostatic latentimages including means for forming images on ordinary insulatingsurfaces are known in the art and may be used instead of the ones shown.

After the sensitizing and exposing steps are completed, thephotosensitive member passes by development station 27 which will bedescribed more fully in conjunction with FIG. 2. Following imagedevelopment, the image is transferred from photosensitive member 11 toweb 37, or the like. Guide rolls 38 and 39 act to position web 37against photosensitive member 11 while transfer is accomplished by asecond corona device 41. Web 37 is fed from reel 34 before transfer andis rewound on reel 36 after transfer and fusing. Fusing element 42 ispositioned to heat the transferred image and thus fix it and permanentlybond it to paper web 37. Cleaning station 43 is made up of rotatingcylindrical brush 44 which contacts any residue image material fromlayer I4 thus readying it for reuse. The above-described process andapparatus are conventional in the art as evidenced in US. Pat. No. 3,l17,89I. Any of the many known equivalents of process or apparatuselements may be employed in connection with the present invention.

Referring now to FIG. 2, a latent electrostatic charge pattern placed onphotosensitive member SI by a technique such as that described above isdeveloped by two or more brushes disposed side by side adjacent the pathof the surface bearing the latent image. The present invention requiresat least two brushes; that is, a primary brush and at least onesecondary brush; however, generally speaking, as the speed ofdevelopment is increased, additional secondary brushes are desirable toassure the best possible image quality. For the purpose of theembodiment shown in FIG. 2, four brushes 53, 54, 56 and 57 are used andare all contained within housing 52. These brushes can be made of anysuitable material which has the ability to carry toner particles to thesurface bearing the latent image; for instance, magnetic brushes orbrushes made of rabbit fur. The fur brushes as shown in FIG. 2 can begrounded, or, in the alternative, biased with a polarity opposite thepolarity existing on the toner particles.

Each of the brushes can be loaded individually within the developmentsystem, but it is preferable to load only one brush and have the tonerparticles passed along to the other brushes due to the meshing actionbetween the brushes. If magnetic brushes were used, each brush would beloaded individually to assure toner reaches all the brushes. Brush 53 isthe primary brush in the system, it being called primary because it isthe only brush which is loaded with toner particles by external means.

Housing 52 has a loading hopper, generally designated as 60, whichplaces toner particles 55 in the vicinity of the lowest developmentbrush; i.e., primary brush 53. The toner can be fed to the brush in anysuitable manner such as merely having the brush pass through the hopperof toner. In the alternative, the toner particles contained in thehopper can be separated from fur brush 53 by mesh material 61. This meshmaterial should have apertures which are large enough to permit theindividual toner particles to pass through readily and can be made ofany suitable material such as nonconductive brass or the like. If thescreen is made ofa material such as brass, after the toner is placed onthe fibers of brush 53, but before they are deposited on the latentelectrostatic charge pattern, the particles should be exposed to acharging means so that they possess a uniform charge. One simpleapparatus to create such a charge is a triboelectric generator placed inthe path of the fibers which rubs against the toner particles beforethey contact the surface being developed.

Another system utilized to place a uniform charge on the toner particlesis shown in FIG. 2. Mesh material 61 is made of a material which istriboelectrically related to toner particle material so that as thefibers on fur brush 53 rub against the mesh material, the individualparticles of toner are brought through and rub against the mesh materialand receive a charge triboelectrically.

The position of the primary brush relative to the direction of travel ofthe surface being developed is of importance in the present invention.The primary brush; i.e., brush 53, is the brush which initially contactsthe surface being developed, and, consequently, the brush which depositsthe bulk of the toner on the latent image. When a rotary drum is beingdeveloped, as in FIG. 2, the primary brush is the lowest brush in thesystem. The significance of developing in such an uphill" fashion willbe explained hereafter.

In FIG. 2, the drum is shown as rotating in the counterclockwisedirection and since the primary brush is the first brush to develop, itmust be the lowest brush in the system.

Similarly, if a flatplate were the surface bearing the latent image, theplate should be developed while traveling on an incline to thehorizontal and the primary brush would again be the lowest brush.

Toner particles that brush 53 picks up from screen 61 are brought aroundto the photosensitive surface where they develop the latent image.Brushes 53, 54, 56 and 57 are placed closely adjacent each other so thatas they turn their fibers mesh. By this action, a portion of the tonerwhich is picked off the screen by brush 53 and which is not deposited onsurface 51 is transferred to brush 54. Likewise, a portion of the tonerwhich is held by the fibers of brush 54 and is not deposited on thephotosensitive surface by brush 54 is transferred onto brush 56. Similartransfer of toner particles occurs between brush 56 and 57 and any otherbrushes in the group. In this manner all the development brushes areloaded with toner particles and participate in the development process.

The reason for developing in an uphill" fashion, as mentioned above, isto keep the toner particles circulating throughout the hopper during thedevelopment process. Flicker bar removes any toner particles from brush57 after the fibers have come into contact with the surface beingdeveloped. Therefore, brush 57 is not allowed to become saturated withtoner and acts as a semidevelopment, semicleaning brush which depositstoner particles where they are needed and cleans background areas wheretoner particles are not desired. After removing the excess tonerparticles'from brush 57 by a flicker bar at the position shown in FIG.2, the toner particles roll down the housing and onto the primary brushthereby circulating the unused toner particles and keeping most of thetoner on the primary development brush. The use of the flicker bar isoptional.

The use of more than one brush to develop the latent image serves atwofold purpose in the present invention. The first purpose is to permitadequate toner deposit when the surface bearing the latent electrostaticcharge pattern is rotating at high speeds. Good development resultsbecause of the increased contact area between the brushes and thephotosensitive surface due to the increased number of brushes. Inaddition to the increased contact area, the meshing of fibers onadjacent brushes generates a small powder cloud in the development areawhich increases the efficiency of development of solid areas in theimage. Further, the meshing of fibers on adjacent brushes prevents thefibers from becoming matted and, hence, they remain efficient carriers.The second purpose for using multiple development brushes is toapproximate the most efficient method of development; that is,developing the latent electrostatic charge pattern by imparting aswirling mo tion while depositing toner particles on the latent image.The use of a multitude of fur brushes as shown in FIG. 2 approxi matesthis motion. This motion is accomplished by two features in the movementof fur brushes. The first feature is that each brush in the group isoscillated coincident with its axis of rotation as it is rotated. Inother words, each brush is oscillated side to side, or towards and awayfrom the observer of FIG. 2. It is preferred that each brush beoscillated in a different direction compared to brushes adjacent it atany given instant for two reasons. First, such alternating motionincreases the meshing and twisting of the individual toner-laden fiberswhich increases the swirling action. Secondly, it is easier todynamically balance the development system in this fashion.

The second feature in the movement of the brushes is that all thedevelopment brushes in the system are not rotated at the same speed. Inpractice, brushes 53, 54, 56 and 57 shown in FIG. 2 may be rotated attotally different speeds from one another. However, due to pragmaticconsiderations, the brushes are rotated at set speeds in order toachieve optimum results in a high-speed system. The first considerationin a system using rabbit fur brushes and conventional toner; i.e., apigment such as carbon black dispersed in thermoplastic, is the speed ofthe photosensitive surface being developed. For the purposes of thisdisclosure it will be assumed that the latent image is produced in ahigh-speed xerographic machine on a drum whose surface speed isapproximately 40 inches/second.

Optimum quality during the development with a fur brush ordinarilyoccurs when the peripheral speed of the fur brush approximates theperipheral speed of the surface being developed, the brush rotatingabout its axis in the opposite direction as the photosensitive member.Also, when many brushes are used in a development system, simpler andless costly brush drive systems are possible when the various speeds ofthe brushes are kept to a minimum number.

Taking these two considerations into account in the apparatus shown inFIG. 2, the preferred speed of brushes 53 and 56 is 42-46 inches persecond in the clockwise direction while brushes 54 and 57 rotate 3438inches per second in the clockwise direction. These speeds are preferredsince experiments indicate that a variance of from 4-12 inches persecond between adjacent brushes result in superior images. Therefore,primary brush 53 and brush 56 have a peripheral speed slightly fasterthan the peripheral speed of surface 51 and tend to brush the surfacewhereas brushes 54 and 56 have a speed slightly slower than the surfacebeing developed and tend to drag on the surface.

It should be reiterated at this point that the above brush speeds anddirections of rotation are merely sample speeds and are not critical tothe operation of the invention. For instance, brushes 54 and 57 could berotated in the counterclockwise direction while brushes 53 and 56 rotatein the clockwise direction and the system would still be operative. Themajor consideration in the invention is that adjacent brushes mesh witheach other and rotate at different speeds relative to each other.

Cleaning brush 58 bears against photosensitive surface 51 at a pointremoved from development brushes 53, 54, 56 and 57. This cleaning brushdoes not mesh with any of the other brushes in the system and interfereswith the photosensitive surface only after it has passed through thedevelopment area. The purpose of this brush is to remove backgroundtoner from the developed image. Brush 59 acts as a sealing brushcatching any toner that leaks from the development area in the directionopposite the direction of rotation of the photosensitive surface and ismost desirable in high speed systems. Toner particles caught by thisbrush are placed on the photosensitive surface in imagewiseconfiguration by brush 59. Both cleaning brush 58 and sealing brush 59are optional in the apparatus shown.

In addition to the method outlined above many other modifications and/oradditions to this invention will be readily apparent to those skilled inthe art upon reading this disclosure, and these are intended to beencompassed within the scope of the invention.

What is claimed is:

1. In a development apparatus for applying electrically charged tonerparticles to a moving surface bearing a latent electrostatic imagecomprising a primary rotatable brush adapted to initially contact theimage and at least one sec0ndary rotatable brush wherein the brushescontact the surface for applying toner particles thereon, and whereinthe bristles of the secondary brush are in interference with thebristles of the primary brush, means for imparting rotative peripheralmovement to the primary brush and means for loading the outer peripheryof the primary brush with toner particles, the improvement comprising,

means for imparting rotative peripheral movement to the secondary brushand at a speed different than the speed of the rotative movement of thefirst brush.

2. In a development apparatus for applying electrically charged tonerparticles to a moving surface bearing a latent electrostatic imagecomprising a primary rotatable brush adapted to initially contact theimage and at least one secondary rotatable brush wherein the brushescontact the surface for applying toner particles thereon, and whereinthe bristles of the secondary brush are in interference with thebristles of the primary brush, means for imparting rotative peripheralmovement to the primary brush and means for loading the outer peripheryof the primary brush with toner particles, the improvement comprising,

means for imparting rotative peripheral movement to the secondary brushand at a speed different than the speed of the rotative movement of thefirst brush, said rotative movement of the secondary brush being in adirection opposite that of the rotative movement of the primary brush.

3. The apparatus of claim ll wherein the speed of said rotative movementof the primary brush is greater than the speed of movement of thesurface and the speed of rotative movement of the secondary brush isless than the speed of movement of the surface.

4. in a method of developing a surface bearing a latent electrostaticcharge pattern with charged toner particles which comprises the steps ofcontacting at least two brushes having their bristles in interferringrelationship, one being a primary brush arranged to initially contactthe pattern and the other being a secondary brush, loading the primarybrush with toner particles, moving the surface relative to and ininterference with the brushes whereby the first brush to contact thepattern is the primary brush, simultaneously oscillating the brushes ina plane parallel to the plane of the surface and perpendicular to themovement of the surface, the improvement comprising:

imparting rotative peripheral movement to each of said brushes and atspeeds wherein the rotative movement of said primary brush is differentthan the speed of rotative movement for the secondary brush.

2. In a development apparatus for applying electrically charged tonerparticles to a moving surface bearing a latent electrostatic imagecomprising a primary rotatable brush adapted to initially contact theimage and at least one secondary rotatable brush wherein the brushescontact the surface for applying toner particles thereon, and whereinthe bristles of the secondary brush are in interference with thebristles of the primary brush, means for imparting rotative peripheralmovement to the primary brush and means for loading the outer peripheryof the primary brush with toner particles, the improvement comprising,means for imparting rotative peripheral movement to the secondary brushand at a speed different than the speed of the rotative movement of thefirst brush, said rotative movement of the secondary brush being in adirection opposite that of the rotative movement of the primary brush.3. The apparatus of claim 1 wherein the speed of said rotative movementof the primary brush is greater than the speed of movement of thesurface and the speed of rotative movement of the secondary brush isless than the speed of movement of the surface.
 4. In a method ofdeveloping a surface bearing a latent electrostatic charge pattern withcharged toner particles which comprises the steps of contacting at leasttwo brushes having their bristles in interferring relationship, onebeing a primary brush arranged to initially contact the pattern and theother being a secondary brush, loading the primary brush with tonerparticles, moving the surface relative to and in interference with thebrushes whereby the first brush to contact the pattern is the primarybrush, simultaneously oscillating the brushes in a plane parallel to theplane of the surface and perpendicular to the movement of the surface,the improvement comprising: IMPARTING rotative peripheral movement toeach of said brushes and at speeds wherein the rotative movement of saidprimary brush is different than the speed of rotative movement for thesecondary brush.